Theoretical and experimental studies of dissimilar secondary metallurgy methods for improving steel cleanliness

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University of Alabama Libraries

Due to a continual increasing industry demand for clean steels, a multi-depth sampling approach was developed to gain a more detailed depiction of the reactions occurring in the ladle throughout the Ladle Metallurgy Furnace (LMF) processing. This sampling technique allows for the ability for samples to be reached at depths, which have not been able to be captured before, of approximately 1.5 m below the slag layer. These samples were also taken in conjunction with samples taken just under the slag layer as well as in between those samples. Additional samples were also taken during the processing including multi-point slag sampling. The heats were divided in to five key processing steps: Start of heat (S), after Alloying (A), after desulfurization/start of pre-Rinse (R), prior to Ca treatment (C), and End of heat (E). Sampling sets were collected to compare the effects of silicon, desulfurization rates, slag emulsification, slag evolution and inclusion evolution. By gaining the ability to gather multiple depths, it was determined that the slag emulsification has the ability to follow the flow pattern of the ladle deeper into the ladle than previously seen in literature. Inclusion evolution has been shown by numerous researchers; however, this study showed differences in the inclusion grouping and distribution at the different depths of the ladle through Automated Feature Analysis (AFA). Also, the inclusion path was seen to change depending on both the silicon content and the sulfur content of the steel. This method was applied to develop a desulfurization model at Nucor Steel Tuscaloosa, Inc. (NSTI). In addition to a desulfurization model, a calcium (Ca) model was also developed. The Ca model was applied to target a finished inclusion region based on the conditions up to the wire treatment. These conditions included time, silicon content, and sulfur concentration. Due to the inability of this model to handle every process variable, a new procedure was created to provide a real time feedback via SparkDat © software installed in a ThermoFisher 4460 spectrometer.

Electronic Thesis or Dissertation
Engineering, Materials science